If you can manage the time away, there are bargains on the Explorer out of Sydney. Check around for the best price, taking into account credit card fees. RCI Australia does not charge to use an Amex or visa. Many travel agencies do.
Too bad there's not an aggregator site for cruise fares.
Visits isle of pines, mare, Vila and mystery island. Personally, I'd stay on the ship for all except isle of pines.
Ozbargain pissup?